This invention relates to a robot control apparatus and, more particularly, to a robot control apparatus having a novel limiter structure for limiting the operating range of each axis constituting a movable portion of a robot mechanism.
An industrial robot grasps a workpiece by means of a hand, or subjects a workpiece to machining, e.g., welding by a tool such as a torch, mounted at a distal end of an arm. In a robot of this type, ordinarily an operating command is issued by a numerical control (NC) unit installed remotely from the robot mechanism, and servomotor power is delivered to the robot mechanism via a magnetics panel, or the like, so that the arm is operated by the servomotor.
Besides a power system cable, a signal system cable is also provided between the robot mechanism and the control unit for transferring such signals as a brake drive signal, signals from various sensors provided on the hand, and signals from limiter switches for limiting the operating range of each axis constituting the robot arm.
In a conventional industrial robot of the above kind, electric signals are used not only for the servomotor power but also for the limiter switch signals of the respective axes; the limiter switches protect the robot. Since the cables usually are arranged close together, an electrical noise component contained in the servomotor power mixes with the limiter switch signals, as a result of which the robot malfunctions. This effect becomes quite pronounced because the power and signal cables are intermingled and packed closely together particularly within the robot arm.
Furthermore, since the limiter switches employ contact switches, the contacts sustain wear and eventually fail to provide smooth on/off action with prolonged switch use. In addition, owing to wear of an operating member, accidents occur in which the limiter switch does not operate even when a dog is actuated.